As a result of that damage, the emergency cooling system that was in place did not have a chance to get going, and Japan's nuclear authorities were forced to resort to seawater cooling for the reactor.

Hundreds of thousands of people have been evacuated from the area near the reactor, and people have been warned to seal their homes in order to avoid breathing in radioactive dust.

Using sea water to cool the reactor, the power plant's operators have been forced to release radioactive steam produced into the atmosphere.

The radioactive material that is being spewed into the air may end up contaminating food and water resources, according to scientists in Hong Kong.

Lam Ching-wan, a chemical pathologist at the University of Hong Kong, said that the explosions could expose people to longer-term radiation, raising the risk of certain types of cancer.

He said that thyroid cancer, bone cancer and leukaemia were the three most common types of cancer to arise from such radioactive contamination, and that children and foetuses would be especially vulnerable.

Lee Tin-lap, a toxicologist and associate professor at the Chinese University of Hong Kong's School of Medical Sciences, said that no one was currently measuring the levels of radiation in the sea, and that this needed to be done.

He said that the steam that was currently being released into the air would eventually get back into the water, that sea life would be affected, and that drinking water would also eventually be affected.

The Fukushima power plant is located about 100 miles north of Tokyo.

Tokyo Electric, the company that owns the power plant, recently said that it had lost cooling capability at the plant's third reactor site, and reported a third explosion at the nuclear complex this morning.

As a result, there is a chance that one or more of the Fukushima reactors could go into partial meltdown, with grave environmental consequences.

Japan's Chief Cabinet Secretary, Yukio Edano, said that, even though the nuclear reactors at Fukushima had lost their cooling capacity, the nuclear containment vessels holding the reactors in place were intact.

However, after the explosion this morning, one of the reactors' nuclear containment systems was reported to have cracked.

If the reactor containment system is in place, Japan's nuclear crisis will probably not cause a nuclear disaster on the scale of the Chernobyl disaster, in which a nuclear reactor exploded. The disaster went unreported by authorities.

After the Chernobyl reactor exploded, cloud of radioactive dust reached Sweden, where it was finally noticed by Swedish nuclear scientists.

Because the Japanese reactors are all well-contained, it is unlikely that an explosion causing widespread environmental damage will occur.

James Stubbins, a nuclear energy professor at the University of Illinois in the US, said that there was basically no likelihood of a huge fire such as the one at Chernobyl, or of a major environmental release like at Chernobyl.

The earthquake and resultant tsunami that happened last week in northeastern Japan cost thousands of people their lives.

Japanese authorities are planning to distribute iodine tablets to people living near the blast.

Radioactive iodine and radioactive caesium are two of the main dangers presented by radioactive contamination.

The modern human diet is fairly iodine-deprived, and as such the body will incorporate radioactive isotopes of iodine into its metabolic processes without noticing it has done so.

Plants and animals also incorporate radioactive iodine into their constituent biological processes, meaning that once radioactive iodine has made its way into the food chain, it presents humans with a very tangible risk of cancer.

Iodine tablets distributed in the event of nuclear contamination go some way toward helping the body take on enough 'safe' iodine.

However, taking on excessive amounts of iodine has also been linked to hyperthyroidism, and should be avoided.

The International Atomic Energy Agency said that almost any increase in released radiation was a long-term cancer risk.

Radiation expert Jacqueline Williams, a research professor in the department of radiation oncology at the University of Rochester in New York, said that anybody currently working on the Fukushima plant would be exposed to full-body radiation, causing potentially grave injuries to emergency personnel and maintenance personnel.

She said that the best protection people could get from a nearby source of radiation was to get indoors and stay there.

Over the weekend, Japanese government officials acknowledged the threat of multiple meltdowns at the site's three nuclear reactors.

If the temperature of any of the three nuclear reactor cores continues to increase past the point where it can be controlled, the cores could still melt down.